The present invention relates to apparatuses for manufacturing containers. More particularly, the present invention relates to an apparatus for transferring container bodies between stages in a container manufacturing process.
Metal beverage cans are designed and manufactured to withstand high internal pressure—typically 90 or 100 psi. Can bodies are commonly formed from a metal blank that is first drawn into a cup. The bottom of the cup is formed into a dome and a standing ring, and the sides of the cup are ironed to a desired can wall thickness and height. After the can is filled, a can end is placed onto the open can end and affixed with a seaming process.
It has been the conventional practice to reduce the diameter at the top of the can to reduce the weight of the can end in a process referred to as necking. Cans may be necked in a “spin necking” process in which cans are rotated with rollers that reduce the diameter of the neck. Most cans are necked in a “die necking” process in which cans are longitudinally pushed into dies to gently reduce the neck diameter over several stages. For example, reducing the diameter of a can neck from a conventional body diameter of 2 11/16th inches to 2 6/16th inches (that is, from a 211 to a 206 size) often requires multiple stages, often 14.
Each of the necking stages typically includes a main turret shaft that carries a starwheel for holding the can bodies, a die assembly that includes the tooling for reducing the diameter of the open end of the can, and a pusher ram to push the can into the die tooling. Each necking stage also typically includes a transfer turret assembly that receives can bodies from a previous or upstream stage and delivers the can bodies to a subsequent or downstream stage.
Conventional transfer turret assemblies typically include a rotating transfer starwheel that includes a plurality of pockets that each retain a received can body under a vacuum force. The vacuum pressure of each pocket abates once the pocket has rotated to a predetermined angular exit position, at which point the can bodies exit the transfer turret pocket and are received by a complementary starwheel pocket of a downstream station. The vacuum is thus set to abate once the pocket has rotated to an angular position that provides for a transfer time that allows the can body to travel into the complementary pocket of the downstream starwheel as the starwheels rotate at a given rate.
While the vacuum abatement location may provide for accurate transfers at a given rotational speed, the capability to operate die necking processes at variable speeds has become desirable to control the quantity of can bodies produced over a given period of time. Unfortunately, varying the starwheel rotational speeds can remove the exit and intake pockets from proper operational alignment due to the resulting varying transfer times, which can cause can bodies to be dropped or crushed during operation, and may use the vacuum ineffectively by providing a period during which vacuum force is applied but no can is located in the pocket.